Failure of Alloy 625 Mixing Point Tee Connection after in Service for 2 Months in Low Temperature LPG Service

Abstract This paper discusses the failure of an Alloy 625 tee and outlines the significant efforts taken for the root cause investigation, contributing factors, preventive measures. This paper will provide significant information to avoid similar failures within the industry. The process medium for this pressured boundary component is LPG which contains high concentration of chlorides, mercury and presence of moisture. Due to the corrosive nature of these species, the suspected damage mechanism is hydrochloric acid (HCL) corrosion at which the mixing point was then upgraded to Alloy 625 from carbon steel. Upon failure, the Alloy 625 tee exhibited minimal thinning, as expected but two linear indications were found on its tee body. This may suggest the occurrence of stress corrosion cracking on the tee. The mill certificate was reviewed and found to meet all the requirements. The intergranular corrosion test was performed and it was accepted. Detailed failure analysis was performed, and the outcome analysis is presented and discussed in the later section of this paper. The findings provide insights into the challenges of maintaining corrosion resistance of nickel-based alloys in chloride and mercury containing LPG service considering for material qualification and selection of intergranular corrosion (IGC) testing methods.